- file.c split layout retained; security-hardened secure-fs helpers
(open_secure_parent/to_disk_secure/rename_secure/stat_secure) now live in
file.c with file_ prefix and are shared with file_receive.c
- file_receive.c takes the security branch's bounded allocations
(receive_data_limited, data_decompress_limited, size checks) and
STATUS_ERROR signaling
- file_send.c gains the data consistency check on file->data
- client_validation.c: stricter --tls requiring --ca, log_message style
- utils.c: hardened openat/mkdirat mkdir_r from security branch